This invention relates to a marine drive system and, more particularly, to a sleeve to isolate the stainless steel shift shaft within the drive.
In a marine drive unit, a gearcase dog clutch is used for shifting the engine. The gearcase dog clutch is coupled to an upper shift shaft portion that is positioned in the center of an exhaust passageway. The shift shaft is made of stainless steel for strength and corrosion resistance.
The shaft is supported on each end by oil impregnated bronze bearings pressed into an aluminum die cast bell housing. The upper bronze bearing abuts an oil seal to limit the entry of sea water into a shift actuator cavity. Above normal sea water temperatures within the bell housing exhaust cavity cause galvanic corrosion of the shaft and erosion of the aluminum housing. The non-functional binding caused by the galvanic corrosion impairs shifting.
Therefore, it is the primary objective of this invention to provide a device to isolate the shift shaft from sea water and to prevent galvanic corrosion and binding of the stainless steel shifting shaft.
It is a further objective of this invention to provide a device which isolates a shift shaft within a marine drive and prevents entry of sea water into the shift actuator cavity.
It is a still further objective of this invention to provide a device for isolating a shift shaft in a marine drive without impairing the shifting function of the engine.
In accordance with the invention, a device is provided which isolates a shift shaft extending through a bell housing in a marine drive system from sea water within the bell housing exhaust cavity. The exhaust cavity has a first bore extending through a bottom wall of the bell housing and a second bore which extends through a portion of the bell housing between the exhaust passage and the shift actuator cavity. The first bore and the second bore are on opposite sides of the exhaust cavity and the shift shaft extends therethrough.
The shift shaft is provided with one or more grooves extending radially about the outer surface of the shaft. It is preferred to have a pair of annular grooves spaced along the shift shaft. A radial seal is located within each spaced annular groove on the shift shaft.
An elongated sleeve, preferably of inert plastic, is provided for receiving the shift shaft therein. The inner diameter of the sleeve is such that each radial seal engages the inner surface of the sleeve thereby preventing air and/or sea water from entering the interior of the elongated sleeve from the shift actuator cavity or from outside of the bell housing. In addition, the interface between the sleeve and the seals acts as a bearing surface for the shaft.
The elongated sleeve extends along the entire length of a portion of the shift shaft. The sleeve has a first end sealably mounted in the first bore and a second end sealably mounted in the second bore. The sleeve is mounted in each bore by use of an adhesive so as to prevent sea water from entering the shift actuator cavity through the first bore or from leaving the bell housing through the second bore.